The present invention relates to novel bisazo compounds and electrophotographic photoconductors comprising the bisazo compounds, and more particularly to novel bisazo compounds and an electrophotographic photoconductor comprising, on an electroconductive support material, a photoconductive layer containing any of the novel bisazo compounds.
Conventionally, a variety of inorganic and organic electrophotographic photoconductors are known. As inorganic photoconductors for use in electrophotography, there are known types, in which the photoconductive material is, for instance, selenium, cadmium sulfide, or zinc oxide. In an electrophotographic process, a photoconductor is first exposed to corona charges in the dark so as to electrically charge the surface of the photoconductor uniformly. The thus uniformly charged photoconductor is then exposed to original light images and the portions exposed to the original light images selectively become electroconductive, so that electric charges dissipate from the exposed portions of the photoconductor, whereby latent electrostatic images corresponding to the original light images are formed on the surface of the photoconductor. The latent electrostatic images are then developed by the so-called toner which comprises a colorant, such as a dye or a pigment, and a binder agent made, for instance, of a polymeric material; thus, visible developed images can be obtained on the photoconductor. It is necessary that photoconductors for use in electrophotography have at least the following fundamental properties: (1) chargeable to a predetermined potential in the dark; (2) minimum electric charge dissipation in the dark; and (3) quick dissipation of electric charges upon exposure to light.
While the above-mentioned inorganic electrophotographic photoconductors have many advantages over other conventional electrophotographic photoconductors, at the same time they have several shortcomings from the viewpoint of practical use.
For instance, a selenium photoconductor, which is widely used at present, meets the above-mentioned three conditions (1) through (3) fairly well, but it has the shortcomings that it is difficult to work it into the form of a belt due to its poor flexibility, and it is so vulnerable to mechanical shocks that it must be handled with the utmost care. Other inorganic electrophotographic photoconductors have similar shortcomings to those of the selenium photoconductor.
Recently, electrophotographic photoconductors, employing a variety of organic photoconductive materials have been investigated, developed in order to eliminate the shortcomings of the inorganic electrophotographic photoconductors and some of them are in fact employed for practical use. Representative examples of such organic electrophotographic photoconductors are an electrophotographic photoconductor having a photoconductive layer comprising poly-N-vinylcarbazole and 2,4,7-trinitro-fluorene-9-one (U.S. Pat. No. 3,484,237); a photoconductor having a photoconductive layer comprising poly-N-vinylcarbazole which is sensitized by a pyrylium salt type coloring material (Japanese Patent Publication No. 48-25658); a photoconductor having a photoconductive layer comprising as the main component an organic pigment (Japanese Laid-Open patent application No. 47-37543); and a photoconductor having a photoconductive layer which contains as the main component an eutectic crytaline complex consisting of a dye and a resin (Japanese Laid-Open patent application No. 47-10735).
Although the above-mentioned organic electrophotographic photoconductors have many advantages over other conventional inorganic electrophotographic photoconductors, in particular, with respect to the mechanical strength and flexibility, they still have several shortcomings from the viewpoint of practical use. In particular, they are relatively low in electrophotographic photosensitivity.
Further, there is known an electrophotographic photoconductor comprising, on an electrically conductive support material, a photoconductive layer which contains an azo compound. An example of such electrophotographic photoconductor is disclosed in Japanese Patent Publication Ser. No. 44-16474, in which a monoazo compound is employed in the photoconductive layer. Another example is an electrophotographic photoconductor employing a benzidine-type bisazo compound, which is disclosed in Japanese Laid-open patent application Ser. No. 47-37543. A further example is an electrophotographic photoconductor employing a bisazo compound having a stilbene skelton, which is disclosed in Japanese Laid-open patent application Ser. No. 53-133445. The above azo compounds are in fact useful materials for the photoconductive layers of electrophotographic photoconductors. However, they also have several shortcomings from the viewpoint of practical use, particularly in terms of photosensitivity and flexibility.